recognized by the Commonwealth). A period of peace lasted from August 1649 to February 1651, but the Polish side balked at the implementation of the Zboriv agreements and further confrontations became inevitable. Khmelnytsky pursued diplomatic activities and obtained a promise of the Ottoman Empire protection and Moldavia's rule for himself upon swearing a fealty oath to the Sultan in 1650. The Cossack Hetman's emissaries also established contacts with Commonwealth dissidents and disaffected peasants in several regions of the Polish Crown and Silesia. The Kostka-Napierski Uprising erupted in June 1651 in the Podhale region. The peasant rebels, influenced by Khmelnytsky and his uprising, took over the Czorsztyn castle, from where their leader Napierski issued universals calling on the peasants to throw off their lord's yoke. The insurgency generated limited following and was soon suppressed, its leaders executed. There were also a few other centers of peasant revolt, including one organized by Piotr Grzybowski in Greater Poland. In February 1651, Hetman Kalinowski advanced against the Cossacks, but suffered heavy losses and withdrew to Kamieniec Podolski; in May he fought his way to Sokal, where he joined the gathering of the Crown army. In June, both the regular army and szlachtas pospolite ruszenie moved decisively against the Tatar-Cossack forces. At the Battle of Berestechko King John Casimir was able to impose on the enemy the site for the confrontation he chose and in heavy fighting destroy the Cossack army, while the fleeing Tatars took Khmelnytsky with them. However, a majority of the Cossack soldiers were saved by one of their outstanding commanders, Ivan Bohun. Berestechko, "one of the greatest achievements of the Polish military", removed the threat to the Commonwealth present since 1648, but brought no resolution to the Ukrainian conflict. The szlachta fighters soon left. Khmelnytsky regrouped and with Tatar reinforcements resumed his military harassment. As the combined Crown and Lithuanian armies were not able to follow up the Berestechko victory in the inconclusive Battle of Bila Tserkva, the two sides signed the Treaty of Bila Tserkva, which reduced the Treaty of Zboriv Cossack gains. With the Sultan's support Hetman Khmelnytsky then attempted to subjugate Moldavia by demanding a marriage of his son Tymofiy to Ruxandra, daughter of Vasile Lupu, the Moldavian ruler connected to the Radziwiłł family. After Vasile's refusal the Hetman sent to Moldavia a strong Cossack-Tatar army. This force was confronted in May 1652 by Hetman Kalinowski and his